1. Field of the Invention
The present invention relates to the motion control of scuba divers, particularly to buoyancy compensators which utilize flexible air bladders to provide control over the vertical motion of a scuba diver.
2. Description of the Prior Art
Buoyancy compensators are used by scuba divers to provide a means of controlling buoyancy while diving. Most, if not all, scuba divers currently use buoyancy compensators which consist of flexible air bladders and hand actuated pneumatic fill and release valves. The buoyancy force acting on the scuba diver is changed by adjusting the volume of air in the buoyancy compensator bladder.
The buoyancy compensators currently available to scuba divers require significant attention, from the diver, to attain and maintain neutral buoyancy, to safely descend, to safely ascend, and to establish adequate positive buoyancy at the surface. Tile diver controls buoyancy by using the hand actuated air valves to iteratively add and release air from the buoyancy-compensator bladder, while observing vertical motion changes by reference to nearby stationary objects or depth gauge readings. The diver also compensates for this coarse buoyancy control by swimming in the vertical direction opposite to the buoyancy force vector error.
Neutral buoyancy, attained by the method mentioned above, is achieved at a single depth and must be adjusted as the depth of the dive changes otherwise a deviation in the buoyancy force will develop. This deviation from neutral buoyancy is due to the volume of air in the bladder changing with changes in the hydrostatic pressure of the water, and thus with changes in the depth the diver. Since the air volume changes in a nonlinear fashion with depth, it is difficult to adjust for the buoyancy changes using hand actuated valves. It is desirable to avoid a negative buoyant condition since this can lead to inadvertent diver contact with fragile reef ecosystems or excessive dive depths. It is also desirable to avoid a positive buoyant condition since this requires the diver swim downward to maintain depth.
In the past, several Letters Patents of the United States have been granted on improvements to buoyancy compensators. The following patents claim to maintain neutral buoyancy as the scuba diver changes depth: U.S. Pat. No. 3,820,348 to Fast, 1974 Jun. 28; U.S. Pat. No. 4,114,389 to Bohmrich et al., 1978 Sep. 19; U.S. Pat. No. 4,324,507 to Harrah, 1982 Apr. 13; and U.S. Pat. No. 4,601,609 to Hyde, 1986 Jul. 22. These inventions are mechanical in nature and utilize springs, cables, and/or rigid volumetric structures to compensate for deviations from neutral buoyancy. Fast and Bohmrich utilize rigid outer shells for their buoyancy compensators, which are more unwieldy than the currently popular and streamlined flexible bladder designs. A limitation in utility of all of these buoyancy compensators is that the diver is required to first attain neutral buoyancy by the same iteration method mentioned above for currently available buoyancy compensators.
Another patent, U.S. Pat. No. 3,487,647 to Brecht, 1970 Jan. 6, provides the diver with a means to achieve neutral buoyancy by depression of a single button and then the rotation of a lever arm. This invention is a complex, mechanically controlled buoyancy compensator that includes: multiple pneumatic valves, springs, a bellows, a rocker arm, a rolling diaphragm, and a piston. Once neutral buoyancy is attained, the diver's vertical position is controlled, by the buoyancy compensator, so that a constant depth is maintained. A disadvantage of this buoyancy compensator is apparent when the diver tries to change depth while in the "constant depth" mode. Brecht's invention automatically changes the diver's buoyancy to maintain the same depth. For example, if the diver wishes to follow the top contour of a reef, then Brecht's invention would counter the diver's vertical motion, forcing the diver to remain at one depth.
One parameter that affects neutral buoyancy with depth changes is the compression and expansion of a diver's exposure suit. Only Fast and Harrah provide a means to compensate for this by including wet suit material inside the compensator mechanisms. A change in the thickness of the wet suit material inside the compensator mechanisms affects the amount of air added or released from the air bladders. Both compensation methods are coarse, at best, since the overall change in buoyancy force also depends on the area of the material used to for the exposure suit. The area of wet suit material depends on the size of the exposure suit as well as which components of the suit are actually being worn by the diver for the dive.
Another parameter that effects the buoyancy of the diver as the dive progresses is the amount of air consumed from the scuba tank. The weight of the air in the scuba tank at the start of the dive is approximately 6 pounds. As the dive progresses, the diver consumes air and the weight of the air in the scuba tank decreases, resulting in an increase in buoyancy. Brecht's invention, with the "constant depth" control mode, is the only prior-art buoyancy compensator which will compensate for the change in buoyancy due to the consumption of air in the scuba tank. But again, Brecht's buoyancy compensator forces the diver to remain at a constant depth.
During the descent of the dive, it is desirable to descend slowly to allow the air spaces in the body of the diver to equalize with the external hydrostatic pressure of the water. The scuba diver accomplishes this by first manually releasing; air from the buoyancy compensator to become negatively buoyant. As the diver descends, the descent rate is controlled by manually adding air to, and releasing air from, the buoyancy compensator, and by kicking upward toward the surface of the water. This manual control, with diver-sensed motion feedback, is required on currently available buoyancy compensators. The buoyancy compensators by Fast, Bohmrich et al., Harrah, and Hyde all provide buoyancy compensation with depth change but all of the prior-art references listed require thee diver's immediate attention to monitor the descent rate and to provide corrective actions, when necessary.
To ascend from a dive, the diver maintains a safe ascent rate by manually releasing air from the buoyancy compensator, while monitoring vertical velocity, and swimming toward the surface. Visual clues or depth gauge readings are used, by the diver, to estimate vertical velocity. Excessive ascent rates can lead to lung over-expansion injury and/or to decompression sickness. All currently available buoyancy compensators, as well as all of the prior art, require the diver's immediate attention and actions to monitor and control the ascent rate.
U.S. Pat. No. 4,437,843 to Birle, 1984 Mar. 20, provides a mechanical apparatus for limiting the ascent rate of an ascending diver. The utility of this invention is limited for vertical motion control, however, since the invention provides no means to support neutral buoyancy control or descent rate control.
A safety stop is routinely performed by scuba divers, during the final ascent from a dive, at a depth of approximately 15 feet. This safety stop provides a few more minutes to expire excess nitrogen from the diver's body, before surfacing. This is yet another precaution taken to avoid decompression sickness. No means is provided by prior art or currently available buoyancy compensators to automatically initiate the safety stop by stopping the diver's vertical motion and establishing neutral buoyancy at the safety stop depth.
Another function of the buoyancy compensator is to provide adequate positive buoyancy for the diver at the surface. This allows the diver to rest comfortably at the surface prior to and following the dive. Adequate positive buoyancy is obtained, by current buoyancy compensators and by prior art, using the hand actuated pneumatic valves to add air to the buoyancy compensator.
Scuba divers typically add weight to themselves, for example using a belt with lead weights, to provide sufficient negative buoyancy to allow them to sink from the surface while donning an empty buoyancy compensator and an exposure suit. It is desirable to use the minimum weight possible since this provides the best buoyancy control. More weight than necessary requires a larger air volume in the buoyancy compensator to balance the gravitational and buoyancy forces. The larger the air volume, the more the buoyancy force changes with depth, and the more difficult it becomes to compensate for it using hand actuated valves. The tendency, however, is to dive with more weight than is required to avoid the trial and error process of entering and exiting the water until the correct weight is determined. This further reduces the accuracy of buoyancy compensation using current buoyancy compensators.